[bug report] mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Qi Zheng,

Commit e3aafd2d3551 ("mm: pgtable: reclaim empty PTE page in
madvise(MADV_DONTNEED)") from Dec 4, 2024 (linux-next), leads to the
following Smatch static checker warning:

	mm/pt_reclaim.c:69 try_to_free_pte()
	error: uninitialized symbol 'ptl'.

mm/pt_reclaim.c
    35 void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr,
    36                      struct mmu_gather *tlb)
    37 {
    38         pmd_t pmdval;
    39         spinlock_t *pml, *ptl;
    40         pte_t *start_pte, *pte;
    41         int i;
    42 
    43         pml = pmd_lock(mm, pmd);
    44         start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl);
    45         if (!start_pte)
    46                 goto out_ptl;

ptl is uninitialized on error.

    47         if (ptl != pml)
    48                 spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
    49 
    50         /* Check if it is empty PTE page */
    51         for (i = 0, pte = start_pte; i < PTRS_PER_PTE; i++, pte++) {
    52                 if (!pte_none(ptep_get(pte)))
    53                         goto out_ptl;
    54         }
    55         pte_unmap(start_pte);
    56 
    57         pmd_clear(pmd);
    58 
    59         if (ptl != pml)
    60                 spin_unlock(ptl);
    61         spin_unlock(pml);
    62 
    63         free_pte(mm, addr, tlb, pmdval);
    64 
    65         return;
    66 out_ptl:
    67         if (start_pte)
    68                 pte_unmap_unlock(start_pte, ptl);
--> 69         if (ptl != pml)
                   ^^^
Uninitialized variable

    70                 spin_unlock(pml);
    71 }

regards,
dan carpenter